A. Use of Forceplates in Biofeedback Training of Balance
The design and use of forceplates to measure the forces exerted by the feet of a standing subject and the relations between these forces and the subject's balance are well described in the prior art. Examples of these prior art descriptions include: Nashner, L. M., Sensory Feedback in Human Posture Control, Massachusetts Institute of Technology Report MVT-70-3 (1970), and Black, F.O., et al., "Computerized screening of the human vestibulospinal system," Annals of Otology Rhinology and Laryngology, vol. 87, pp. 783-789 (1978). U.S. Pat. No. 4,136,682 to Pedotti describes a forceplate system on which a standing subject walks, and also includes methods for processing the resulting information relative to the motions of the subject.
The balance of a standing subject is typically characterized in terms of quantities related to the position of the center of force exerted by the feet against the support surface relative to the positions of the feet on the surface. The magnitude and the position of the center of force exerted by a subject standing on a single forceplate, however, is determined in the coordinates of the forceplate support surface. To calculate quantities related to the balance of a subject standing on a single forceplate requires knowledge of the positions of the two feet relative to the forceplate. When the subject is standing with each foot on a separate independent forceplate, the calculation of quantities related to balance requires additional information of the positions of the two forceplates relative to one another.
B. Biofeedback Training of Erect Standing Balance
The earliest known application of a device and method for biofeedback training of erect standing balance was reported in 1967 by Begbie, C. H., "Some problems of postural sway," in: deReuck A. V. S., Knight J., eds. CIBA Foundation Symposium on Myotatic, Kinesthetic, and Vestibular Mechanisms, London, Churchill Ltd, pp. 80-101 (1967).
The Begbie study used a compliant platform to monitor postural sway during erect standing. When the standing subject swayed forward, backward, or to one side, the resultant reaction forces between the feet and the platform support surface deflected the surface in the direction of the subject's sway. Deflection was measured using a potentiometer, the output of which provided a signal related to the direction and extent of the subject's sway. Applications for the measurement and biofeedback device described by Begbie, however, were limited to tasks in which the subject performed standing with the feet in fixed positions.
The Begbie report described a biofeedback application of the platform device in which an oscilloscope displayed two quantities to the subject. The first quantity displayed the deflection of the platform, allowing the subject to see the direction and extent of his own swaying. The second quantity was a target sway position providing the subject with a performance goal. The report described how the platform and biofeedback display helped patients with vestibular balance disorders by allowing them to substantially reduce their otherwise abnormal postural sway.
The description of a device and method for training a standing subject to modify the distribution of weight load between the two legs was described in 1973 by Herman, R, "Augmented sensory feedback in the control of limb movement," in: Fields, W. S., ed., Neural Organization And Its Relevance to Prosthetics, Miami, Symposia Specialists, pp. 197-215 (1973).
The Herman report described several forms of independent force measuring devices for monitoring the vertical load on each leg. The report further described auditory and visual methods for displaying the distribution of the load to the subject. Biofeedback load displays included a frequency modulated tone signal and an array of independently controlled signal lights. With the audio biofeedback, the frequency of the tone increased or decreased as the load on a selected leg increased or decreased. The pattern of illuminated lights changed to signal changes in leg loading. Like the Begbie device and methods, biofeedback training of loads was limited to tasks in which the subject stood with the feet maintained in fixed positions on the support surface.
The Herman report further described clinical training applications of the leg load devices and methods in which patients with musculoskeletal and neurological disorders were instructed to achieve a desired weight bearing on a selected leg by bring the auditory or visual feedback signal within specified target range.
U.S. Pat. No. 4,122,840 by Tsuchiya et al., entitled "Apparatus for Analyzing the Balancing Function of the Human Body," describes a device and method using biofeedback to train the distribution of loads between the two legs of a standing subject. The device consists of independent vertical load detectors to measure the distribution of loads on the legs and an array of light emitting diodes to visually display actual loads relative to a specified target load signal. With the exception of minor differences in force measuring and display technology, the measurement and biofeedback methods were very similar to those described earlier by Begbie and Herman. Like the Begbie and Herman devices and methods, the Tsuchiya and Ohnishi patent is also limited to standing tasks in which the feet are maintained in fixed positions on a support surface.
C. Other Technologies for Measuring Balance and Movement
A number of technologies in addition to force sensing surfaces are potentially available for calculating and displaying quantities related to performance while an erect standing subject performs movement tasks. Several manufacturers market optically based motion analysis systems which measure subject movements without requiring that the feet be positioned on a force sensing surface. Two examples include the ExpertVision system by MotionAnalysis Corp., Santa Rosa, Calif. and the Vicon system by Oxford Medilog Systems Limited, Oxfordshire, England. These technologies, however, are substantially more expensive than force sensing surfaces. These optical motion analysis technologies are not appropriate for routine clinical training, because they require considerable time and technical expertise to calibrate body mounted position targets.
A second potential technology for measuring quantities related to the performance of a standing subject is the shoe instrumented with force sensing devices. An example of such a system is the Computer Dyno Graph (CDG) marketed by Infotronic Medical Engineering of Tubbergan, The Netherlands. For routine clinical use, this type of system also has the disadvantage of also requiring body mounted hardware and calibration. In addition, since these devices do not include means for determining the positions of the force sensing shoes on a continuous basis, they cannot be used to calculate quantities related to the subject's balance.
D. Clinical Applications of Balance Biofeedback Training
A number of published research reports have described clinical applications for balance training devices in accordance with the original concepts described by Begbie and Herman. Balance training was used to achieve symmetrical standing in stroke patients. Wannstedt, G. T., et al., "Use of augmented sensory feedback to achieve symmetrical standing," Physical Therapy, vol. 58, pp. 553-559 (1978). Similar devices were used to train children with cerebral palsy. Seeger, B. R., et al., "Biofeedback therapy to achieve symmetrical gait in children with hemiplegic cerebral palsy," Archives of Physical Medicine and Rehabilitation, vol. 64, pp. 160-162 (1983). Two additional studies used balance biofeedback therapy to reestablish the stability of stance and gait in hemiplegic patients. Shumway-Cook, A., et al., "Postural sway biofeedback: its effect on reestablishing stance stability in hemiplegic patients," Archives of Physical Medicine and Rehabilitation 69:395-400 (1988); and Winstein, C. J., et al., "Standing balance training: effect on balance and locomotion in hemiplegic adults," Archives of Physical Medicine and Rehabilitation, vol. 70, pp. 755-762 (1989). Additional studies using biofeedback training in standing patients include: Clarke, A. H., et al., "Posturography with sensory feedback--a useful approach to vestibular training?," in: Brandt, T., et al., eds., Disorders of Posture and Gail , Stuttgart, George Thieme Verlag, pp. 281-284 (1990); Jobst U., "Patterns and strategies in posturographic biofeedback training," in: Brandt, T., et al., eds., Disorders of Posture and Gait, Stuttgart, George Thieme Verlag, pp. 277-300; Hamann, K. F., et al., "Clinical application of posturography: body tracking and biofeedback training," in: Brandt, T., et al., eds., Disorders of Posture and Gait, Stuttgart, George Thieme Verlag, pp. 295-298 (1990); and Hamman, R. G., et al., "Training effects during repeated therapy sessions of balance training using visual feedback," Archives of Physical Medicine and Rehabilitation, vol. 73, pp. 738-744 (1992).
The most recent clinical study is Sackley, C. M., et al., "The use of a balance performance monitor in the treatment of weight-bearing and weight-transference problems after stroke," Physiotherapy, vol. 78, pp. 907-913 (1992). This article describes clinical applications of a system comprised of two independent force-measuring footplates. The article describes training tasks in which the patient stands in-place on the footplates, rises from a chair onto the footplates, and transfers weight between two footplates, one at floor level and the other on a higher step surface.
While the Sackley, et al., article is the first to describe the measurement and biofeedback display of leg loading information during weight transfers to different step heights and during rises from a chair, the described devices and methods cannot measure or display quantities related to the subject's balance during performance of these tasks. This is because the device does not include means for calculating the position of the center of force relative to the positions of the two feet. Specifically, the operations leading to calculation of the display quantities do not take into account the positions of the feet on the footplates or the positions of the footplates.
The Sackley, et. al., device and methods do not permit the calculation and biofeedback display of quantities related to balance during the sit to stand movement. Because the device does not include means for measuring the forces exerted by the buttocks against the seat surface, quantities related to the subject's balance cannot be calculated when a portion of the subject's weight is supported by the chair surface. Additionally, the operations leading to calculation of the display quantities do not take into account the positions of the footplates relative to the chair surface.
E. Equipment for Balance Biofeedback and Mobility Training
A number of manufacturers market equipment to train patients in standing movement tasks which reproduce daily life functions. Clinical equipment of this type includes adjustable height steps for the training of stepping and stair climbing, for examples: The Step, model number 4227E; Superstep, model number 8362E; One-Sided Stairs, model number 5638E, all marketed by FlagHouse, Inc., Mt. Vernon, N.Y. Currently marketed products for exercising life-like standing tasks, however, do not incorporate the means to measure or display quantities related to the balance performance of subjects or to provide subjects with performance goals.
Several manufactures now market devices for the assessment and biofeedback training of weight bearing and balance while patients stand erect with the feet maintained in fixed positions on a support surface. In the United States for example, the Balancemaster system manufactured by NeuroCom International, Inc. of Clackamas, Oreg. uses signals from a forceplate to calculate the position of the subject's body center of gravity (COG) over the feet. The COG is displayed on a video monitor along with one or more position targets selected by the clinician. When operating in the training mode, the subject is instructed to shift body position to move the COG into one or a sequence of several targets. In the assessment mode, the speed and accuracy with which the subject moves the COG to targets are calculated.
The Balance System manufactured by Chattecx division of Chattanooga Corporation of Chattanooga, Tenn. uses four vertical force measuring plates to determine the percentage of body weight carried by the front and back portions of each foot. The feedback display and training operations of the device are similar to the NeuroCom system in that a single target indicating the position of the body weight relative to the feet is displayed on a video monitor relative to additional targets.
The Balance Performance Monitor (BPM) is manufactured by SMS Healthcare, Essex CM19 5TL, England. The system consists of two force-measuring footplates and a visual display. Each footplate measures total weight as well as the front-back distribution of the weight. The footplates are movable and can be placed at different locations or surfaces of different heights. The computational means, however, determines only the distribution of weight between the two footplates, independent of the positions of the two plates. Thus, the system does not include computational means to calculate and display quantities related to the balance of the subject under a variety of task conditions.
A number of manufacturers have market devices for assessing and training the strength and range of motion about selected joint of both the arms and legs. The Cybex Extremity Systems manufactured by Cybex division of Lumex, Inc., of Ronkonkoma, N.Y., measures and displays to the subject torsional forces exerted by a number of extremity joints including the ankle, knee, and hip. Forces can be measured as the subject exerts effort against an immovable load (isometric) and while the joint moves a constant velocity (isokinetic). Similar extremity strength training systems are marketed as the Kintron multijoint system by the Chattanooga Group, Inc., of Hixon, Tenn. the Lido Active Multijoint by Loredan Biomedical Inc., of West Sacramento, Calif., and the Biodex Multi-joint Strength Training System by Biodex Medical Systems Inc., of Shirley, N.Y. While all of these systems allow joint strength assessment and training during active movements, none are able to assess and train performance in standing, weight bearing tasks, and none are able to assess and train coordination and strength skills related to balance.
A number of research reports have described chairs instrumented with force measuring devices to quantify the forces associated with sitting and rising from a chair. The earliest known study used forceplates to analyze forces at the knee during the rising movement, Ellis, M. I., et al., "Forces in the knee joint whilst rising from normal and motorized chairs," Engineering Medicine, vol. 8, pp. 33-40 (1979). More recent reports have placed forceplates on both the chair and the floor and have also used motion analysis systems to characterize all of the forces and motions; for example, Alexander, N. B., et al., "Rising from a chair: effects of age and functional ability on performance biomechanics," Journal of Gerontological Medicine, vol. 46, pp. 91-98 (1991). These research devices, however, were not designed to allow the biofeedback training of patients performing sitting and rising movements from a chair.
F. Summary of Background Art
The use of force measuring surfaces to calculate the distribution of forces exerted by the feet relative to the base of support and the biofeedback display of these quantities to train aspects of balance during erect standing with the feet maintained in fixed positions is well established in the prior art. The prior art includes: (1) numerous clinical studies demonstrating applications for balance training with biofeedback and (2) several manufacturers with devices for the biofeedback training of standing in-place balance.
Biofeedback training devices based on forceplate measuring systems available in the present art, however, are useful primarily when the patient performs with the feet maintained in fixed positions. It is possible to use optical motion analysis technology to calculate quantities related to a subject's balance during standing movement tasks such as stepping, stair climbing, and sitting and rising from a chair without requiring the feet be maintained in fixed positions. These optical motion analysis technologies, however, are expensive and require highly technical setup and calibration procedures which are too complex for use in mainstream clinical training applications.
Biofeedback training products are also available in the present art for the assessment of extremity strength during active limb movements. None of these products, however, allow assessment and training of coordination and strength skills when the leg is in the standing weight bearing condition, and none permit training of these skills in relation to balance.